Electrical Circuit Load Calculator

ANA›Life Services Authority›National Calculator Authority›Electrical Circuit Load Calculator

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Electrical Circuit Load Calculator

Calculate electrical circuit load parameters including current draw, power consumption, resistance, and voltage drop for both AC and DC circuits.

Circuit Type

DC (Direct Current) AC Single-Phase AC Three-Phase

Supply Voltage (V)

Load Power (W)

Power Factor (0.01 – 1.00)

One-Way Wire Length (m)

Wire Gauge (AWG)

14 AWG (2.08 mm²) 12 AWG (3.31 mm²) 10 AWG (5.26 mm²) 8 AWG (8.37 mm²) 6 AWG (13.30 mm²) 4 AWG (21.15 mm²) 2 AWG (33.62 mm²) 1 AWG (42.41 mm²) 1/0 AWG (53.49 mm²)

Calculate

(function() { // Resistance per meter (Ω/m) for copper wire at 20°C, both conductors (round trip) // Values: resistivity of copper ≈ 1.724e-8 Ω·m // R/m = (resistivity / cross-section) * 2 (round trip) const AWG_AREA_MM2 = { 14: 2.08, 12: 3.31, 10: 5.26, 8: 8.37, 6: 13.30, 4: 21.15, 2: 33.62, 1: 42.41, 0: 53.49 }; const COPPER_RESISTIVITY = 1.724e-8; // Ω·m

window.eleToggleAC = function() { const type = document.getElementById('ele-circuit-type').value; const pfGroup = document.getElementById('ele-pf-group'); pfGroup.style.display = (type === 'dc') ? 'none' : 'block'; };

window.eleCalc = function() { const resultDiv = document.getElementById('ele-result'); const type = document.getElementById('ele-circuit-type').value; const V = parseFloat(document.getElementById('ele-voltage').value); const P = parseFloat(document.getElementById('ele-power').value); const pfRaw = document.getElementById('ele-pf').value; const L = parseFloat(document.getElementById('ele-wire-length').value); const awg = document.getElementById('ele-wire-gauge').value;

// --- Validation --- if (isNaN(V) || V ⚠ Please enter a valid positive Supply Voltage.'; return; } if (isNaN(P) || P ⚠ Please enter a valid positive Load Power.'; return; } if (isNaN(L) || L ⚠ Please enter a valid positive Wire Length.'; return; }

let pf = 1.0; if (type !== 'dc') { pf = parseFloat(pfRaw); if (isNaN(pf) || pf 1.0) { resultDiv.innerHTML = '⚠ Power Factor must be between 0.01 and 1.00.'; return; } }

// --- Wire resistance (round trip) --- const areaMm2 = AWG_AREA_MM2[awg]; const areaM2 = areaMm2 * 1e-6; // Round-trip resistance = resistivity * (2 * L) / area const R_wire = COPPER_RESISTIVITY * 2 * L / areaM2; // Ω

// --- Current Calculation --- // DC: I = P / V // AC 1-phase: I = P / (V * pf) // AC 3-phase: I = P / (√3 * V * pf) let I, S, Q; if (type === 'dc') { I = P / V; S = P; Q = 0; } else if (type === 'ac-single') { S = P / pf; // Apparent power (VA) Q = Math.sqrt(SS - PP); // Reactive power (VAR) I = S / V; } else { // Three-phase: S = √3 * V_line * I S = P / pf; Q = Math.sqrt(SS - PP); I = S / (Math.sqrt(3) * V); }

// --- Voltage Drop --- // DC / AC 1-phase: Vdrop = I * R_wire // AC 3-phase: Vdrop = √3 * I * R_wire (line-to-line) let V_drop; if (type === 'ac-three') { V_drop = Math.sqrt(3) * I * R_wire; } else { V_drop = I * R_wire; } const V_drop_pct = (V_drop / V) * 100; const V_load = V - V_drop;

// --- Load Resistance (equivalent) --- const R_load = V / I; // Ω (impedance for AC)

// --- Power Loss in wire --- const P_loss = I * I * R_wire; // W

// --- NEC 80% rule check ---
// Typical breaker ratings for common wire gauges
const BREAKER_AMPS = { 14:15, 12:20, 10:30, 8:40, 6:55, 4:70, 2:95, 1:110, 0:125 };
const breaker = BREAKER_AMPS[awg];
const nec80 = breaker * 0.80;
const necOk = I isNaN(n) ? 'N/A' : n.toFixed(d);
const warn = V_drop_pct > 3
? '⚠ Voltage drop exceeds 3% — consider larger wire or shorter run.'
'✔ Voltage drop within 3% limit.';
const necWarn = !necOk
? ⚠ Current (${fmt(I)} A) exceeds 80% of ${breaker}A breaker (${nec80}A NEC limit).
✔ Current within NEC 80% continuous load rule (≤ ${nec80}A for ${breaker}A breaker).;

const typeLabel = type === 'dc' ? 'DC' : type === 'ac-single' ? 'AC Single-Phase' : 'AC Three-Phase';

let html = ` ### Results — ${typeLabel}

Current Draw (I)${fmt(I, 3)} A Load Impedance / Resistance${fmt(R_load, 3)} Ω Wire Resistance (round-trip)${fmt(R_wire, 4)} Ω Voltage Drop${fmt(V_drop, 3)} V (${fmt(V_drop_pct, 2)}%) Voltage at Load${fmt(V_load, 3)} V Wire Power Loss${fmt(P_loss, 2)} W`;

if (type !== 'dc') { html += **Apparent Power (S)**${fmt(S, 2)} VA **Reactive Power (Q)**${fmt(Q, 2)} VAR **Power Factor**${fmt(pf, 2)}; }

html += ${warn}${necWarn}; resultDiv.innerHTML = html; }; })();

#### Formulas Used

DC Current: I = P / V

AC Single-Phase Current: I = P / (V × PF)  |  S = P / PF  |  Q = √(S² − P²)

AC Three-Phase Current: I = P / (√3 × V × PF)

Wire Resistance (round-trip): R = ρ × 2L / A   where ρCu = 1.724 × 10⁻⁸ Ω·m

Voltage Drop (DC / 1-phase): Vdrop = I × Rwire

Voltage Drop (3-phase): Vdrop = √3 × I × Rwire

Wire Power Loss: Ploss = I² × Rwire

#### Assumptions & References

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References

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